(Bloomberg) -- Chances are low that human-to-human spread of bird flu occurred in a group of people who were exposed to a patient infected with the virus in Missouri, US health authorities said.
The Centers for Disease Control and Prevention is assisting Missouri health officials in its investigation of seven people who began experiencing symptoms after contact with the H5N1-infected patient.
“CDC believes the likelihood of any of the patient’s contacts becoming infected is low, because the patient had such low levels of virus in their respiratory specimen,” the spokesperson said in an emailed response to questions from Bloomberg News.
Concerns about the spread of bird flu are rising as the virus infects birds, dairy cows and a small number of people across the US.
The H5N1 bird flu strain has been recognized as a pandemic threat and has caused human deaths in years past. However, most human cases of the current version have stemmed from exposure to sick animals, causing only mild illness.
The cluster of possible infections surrounds the Missouri case, the first person known to contract H5N1 bird flu in the US without prior exposure to a sick animal. That infection was identified through routine seasonal flu surveillance.
No bird flu infections have been reported in Missouri’s dairy herds or poultry.
Officials are testing several health-care workers and one household contact of the infected person for signs of an earlier immune response to the virus. One health-care worker who came into contact with the patient tested negative. Some developed mild respiratory symptoms, all of which resolved, which could have been caused by a number of other pathogens, the CDC said.
The agency is testing for antibodies that would indicate an immune reaction to H5N1, and expects results in the coming weeks. There are no other signs of human-to-human transmission and no additional human cases of H5N1 influenza in Missouri, the CDC spokesperson said.
In the unlikely event that the tests come back positive, it would be a definitive sign of person-to-person spread, said Richard Webby, a bird flu researcher at St. Jude Children’s Research Hospital in Memphis. There have been no changes in the virus known to enhance its ability to infect or spread between people, the CDC spokesperson said.
There have been 14 reported human cases of H5N1 bird flu in the US in 2024. The source of the latest infection in Missouri is yet to be determined.
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